Flat lighting arrangements which emit homogeneous light in a predetermined direction are gaining increased importance. One exemplary and nonexclusive application of such a lighting arrangement is in a so-called backlight unit (BLU) for high-resolution color flat display screens. Alternative applications are general lighting systems and, in particular, lighting systems for motor vehicles.
The basic requirements for the emission characteristics of a BLU are, for example in the case of liquid-crystal display screens (LC displays), dictated by the general quality criteria for currently available product types, and in particular by the technology of the imaging LC panels used. They may be described as follows: the light should be emitted as a well-collimated, spectrally defined light beam which keeps its properties constant over the entire face of the BLU, so that uniform illumination of the entire LC panel from a principal direction is achieved. The principal direction of the lighting is the normal to the LC panel face in the case of conventional LCDs for 2D viewing and, in the case of special directional BLUs which have been developed for autostereoscopic 3D viewing, is horizontally tilted in one direction.